7. Project Summary/Abstract Circadian clocks have recently become recognized as modulators of a wide array of physiological processes, including glucose homeostasis, blood pressure modulation, and cancer. In addition, it is well established through epidemiological studies that circadian disruption increases the incidence of several types of cancer. However, the molecular basis for these phenomena is not well understood. The underlying hypothesis of this proposal is that the circadian clock component protein Cry2 modulates cancer risk by promoting the destruction of a well-known cancer causing protein, the proto-oncogene c-Myc, and that environmental circadian disruption due to shift work or chronic jet lag enhances cancer risk by altering Cry2 expression leading to increased c-Myc activity. Advancing our functional understanding of these interactions may highlight new therapeutic and regulatory strategies for preventing and/or treating disease. Our previous studies identified the circadian clock component cryptochromes (Cry1 and Cry2) as nutrient and DNA damage responsive transcriptional regulators by virtue of their susceptibility to phosphorylation by AMP-activated protein kinase (AMPK) and DNA damage-induced deubiquitination by Herpes virus associated ubiquitin specific protease (Hausp, a.k.a. Usp7). Most recently, we made the unexpected discovery (described in preliminary data here) that Cry2 is a required physical component of a complex that regulates the stability of c-Myc by targeting it for destruction by the proteasome. In the course of our studies, we have generated unique tools and expertise that enable us to use biochemical, genetic, molecular and physiological approaches to uncover the roles of circadian clocks and of the circadian protein Cry2 in cell growth and tumor development, specifically aimed at asking: 1) Does human CRY2 protect cells from transformation by promoting degradation of MYC family proteins? 2) What is the relative importance of repression and proteolysis in the biological functions of Cry2? and 3) Is disruption of Cry2-dependent Myc turnover involved in increased tumorigenesis caused by chronic jet lag or shift work?